A current sensor utilizing a magnetoelectric transducer is known. The magnetoelectric transducer measures an intensity of a magnetic field generated by a current flowing in a conductor. A unique relationship resides between a magnitude of the current flowing in the conductor and the generated magnetic field. The current sensor uses this relationship to specify a magnitude of the current flowing in the conductor from the intensity of the magnetic field measured by the magnetoelectric transducer.
When a magnetic field other than that generated by the measurement target conductor is sensed by the magnetoelectric transducer, measurement accuracy of the current decreases. Hereinbelow, a magnetic field other than the “magnetic field generated by the measurement target conductor” will be termed “noise magnetic field”. The magnetoelectric transducer and the conductor are proposed to be arranged between a pair of magnetism shield plates so as to shield the magnetoelectric transducer from the noise magnetic field. Japanese Patent Application Publication No. 2013-117447 (hereinbelow, Patent Document 1) discloses an example of such a current sensor.
Patent Document 1 points out the following features. As a result of the noise magnetic field being absorbed by the pair of magnetism shield plates, magnetic flux flows in the respective magnetism shield plates, and a magnetic field is generated between the pair of magnetism shield plates. If the magnetoelectric transducer senses the magnetic field generated between the pair of magnetism shield plates, current measurement accuracy is reduced. Patent Document 1 also proposes a technique for reducing an influence of the magnetic field generated between the pair of magnetism shield plates due to the noise magnetic field.
Here, for the sake of explanation, a coordinate system will be defined. A direction along which a conductor extends will be defined as a Y direction, and two directions orthogonal to the direction along which the conductor extends will respectively be defined as an X direction and a Z direction. A direction along which the conductor and the magnetoelectric transducer are aligned will be defined as the Z direction. The denotations of the X direction, the Y direction, and the Z direction may more generally be termed a first direction, a second direction, and a third direction, respectively. Further, for the sake of explanation, a magnetic field that a measurement target generates will be termed a measuring magnetic field. A magnetic field generated between a pair of magnetism shield plates due to the noise magnetic field will be termed an inter-shield magnetic field. Further, the magnetism shield plates may simply be termed shield plates.
The magnetoelectric transducer senses a magnetic field along a certain direction (magnetism sensing direction). The magnetoelectric transducer does not sense magnetic fields along directions orthogonal to the magnetism sensing direction. A magnetic field generated by a conductor extends in a circular shape with the conductor at a center. If a cross section of the conductor is rectangular, the magnetic field generated by the conductor extends in an ellipsoidal shape with the conductor at the center. The conductor extends in the Y-axis direction, and the magnetoelectric transducer is aligned with the conductor in the Z direction. Thus, the measuring magnetic field penetrates the magnetoelectric transducer in the X direction. Due to this, the magnetoelectric transducer is arranged such that its magnetism sensing direction is oriented in the X direction so that the measuring magnetic field and the magnetism sensing direction match each other. Further, a pair of shield plates sandwiches the magnetoelectric transducer and the conductor in the Z direction.
Now returning to the explanation of the technique for reducing the influence of the inter-shield magnetic field disclosed in Patent Document 1, the magnetoelectric transducer in Patent Document 1 is attached to a surface of a sensor substrate. The magnetism sensing direction is oriented in a direction parallel to the surface of the sensor substrate. The sensor substrate is arranged such that the surface on which the magnetoelectric transducer is attached faces the conductor. This surface of the sensor substrate is orthogonal to the Z direction, and the magnetism sensing direction matches the X direction. The pair of shield plates is arranged such that lines formed by facing surfaces (inner surfaces) of the pair of shield plates in a cross section cut along a plane formed by the X axis and the Z axis are line-symmetric relative to a particular line (reference line). The reference line may be termed a symmetric axis. The pair of shield plates is arranged such that their symmetric axis is in contact with the aforementioned surface of the sensor substrate while extending in the X direction. The inter-shield magnetic field (its magnetic flux lines) extends in a curved shape oriented from one of the shield plates to the other of the shield plates, and as such, the inter-shield magnetic field exhibits symmetry relative to the symmetric axis due to the aforementioned arrangement of the pair of shield plates. Thus, an orientation of the inter-shield magnetic field becomes orthogonal to the symmetric axis. On the other hand, the magnetism sensing direction of the magnetoelectric transducer matches the X direction, that is, the direction of the symmetric axis. The direction of the inter-shield magnetic field comes to be orthogonal to the magnetism sensing direction. As a result of this, the influence imposed on the magnetoelectric transducer by the inter-shield magnetic field is thereby suppressed.